The present invention relates to a light emission switching circuit for use in a larynx stroboscope.
A larynx stroboscope is a device in which a flash lamp is made to emit light in synchronization with the vibration of a patient's vocal cords and is used to examine and diagnose vocal cord polyps, cancer of the larynx, etc. In conducting examination with the device, it is of course necessary to direct the output light of the flash lamp onto the vocal cords under examination. This is carried out with the vocal cords still. That is, the operator of the device operates a switch or the like to cause the flash lamp to emit light at a predetermined fixed frequency so as to illuminate the part under examination. Then, during examination, the light emission mode is switched according to whether or not the vocal cords are vibrating. That is, when the vocal cords are vibrating during examination, the flash lamp is caused to emit light in synchronization with their vibration, while when the vocal cords are still, the flash lamp emits light with a predetermined fixed period.
Heretofore, in order for the device to determine when the vocal cords are still, it has been the practice to detect when the average level of a vocal cords vibration signal (a signal following the vibration of the vocal cords) becomes lower than a reference level. However, because the detection time is relatively long, sometimes the vocal cords are completely still before detection is accomplished. In other words, the vocal cords may have stopped vibrating a significant time before the mode in which light is emitted synchronously with the vocal cords vibration is switched over to the mode in which light is emitted with the predetermined period. Also, with the conventional circuit, the light emission of the flash lamp is stopped momentarily immediately before the switching operation. Recently, it has been found desirable to record the motion of the vocal cords on video tape, and in this case the momentary suspension of light emission greatly lowers the quality of the resultant image.